Screenable and strippable solder mask and use thereof

Abstract

A screenable and strippable solder mask composition which contains a polyepoxide or polyimide/amide; a detackifier and a high-temperature resistant filler; and use thereof for protecting predetermined areas on a substrate from the solder deposition.

Having thus described our invention, what we claim is new, and desire to secure by Letters Patent is: 
     
       1. A screenable, strippable solder mask composition containing: A. a film-forming polymer portion in the form of a liquid composition wherein the film-forming polymer is a polyimide/amide or a liquid polyepoxide;   B. a detackifier compatible with the polymer being selected form the group of (1) liquid silicone oil   (2) terpene   (3) terpineol   (4) drying oil, and   (5) mixtures thereof;     C. a solid high temperature resistant filler in an amount sufficient to render the composition removable from the substrate after solder application; wherein the ratio of A:B is about 2:1 to about 1:3, and provided that when A is a polyepoxide liquid, B includes said silicone oil; and wherein said composition is at least substantially free of hardener for said film-forming polymer.     
     
     
       2. The solder mask composition of claim 1 wherein the film-forming polymer is a liquid polyepoxide. 
     
     
       3. The solder mask composition of claim 1 wherein said film-forming polymer is a polyepoxide of epichlorohydrin and bisphenol A. 
     
     
       4. The solder mask composition of claim 1 wherein said polyepoxide has a viscosity of about 400 to about 5000 centipoises at 25° C., and a molecular weight of about 170 to about 250. 
     
     
       5. The solder mask composition of claim 1 wherein said film-forming polymer is a polyimide/amide polymer. 
     
     
       6. The solder mask composition of claim 1 wherein said film-forming polymer portion is a solution of a polyimide/amide in N-methyl-2-pyrrolidone. 
     
     
       7. The solder mask composition of claim 1 wherein said film-forming polymer is a polyimide/amide from pyromellitic dianhydride and 4,4'-diaminodiphenylether. 
     
     
       8. The solder mask composition of claim 1 wherein said detackifier is a liquid silicone oil. 
     
     
       9. The solder mask composition of claim 1 wherein said detackifier is a polydimethylsiloxane. 
     
     
       10. The solder mask composition of claim 1 wherein said detackifier is a terpineol. 
     
     
       11. The solder mask composition of claim 1 wherein said detackifier has a viscosity of about 25 to about 500 centipoises at 25° C. 
     
     
       12. The solder mask composition of claim 1 wherein said filler has a particle size of about 0.1 to about 20 microns. 
     
     
       13. The solder mask composition of claim 1 wherein said filler has a particle size of about 0.1 to about 5 microns. 
     
     
       14. The solder mask composition of claim 1 wherein said filler is selected from the group of ground glass, zinc oxide, silicon dioxide, alumina, high temperature resistant sands, and mixtures thereof. 
     
     
       15. The solder mask composition of claim 1 which has a viscosity of about 700 to about 15,000 centipoises at 25° C. 
     
     
       16. The solder mask composition of claim 1 having a viscosity of about 1000 to about 13,000 centipoises at 25° C. 
     
     
       17. The solder mask composition of claim 1 having a viscosity of about 7000 to about 12,500 centipoises at 25° C. 
     
     
       18. The solder mask composition of claim 1 wherein the ratio of the film-forming polymer of the polymer portion of the composition relative to the detackifier is about 1:1 to about 2:3. 
     
     
       19. The solder mask composition of claim 1 wherein the amount of filler relative to the film-forming polymer component of the polymer portion of the composition is about 1:6 to 6:1. 
     
     
       20. The solder mask composition of claim 1 wherein said detackifier is a natural drying oil. 
     
     
       21. The solder mask composition of claim 1 wherein the amount of filler relative to the film-forming polymer component of the polymer portion of the composition is about 2:1 to about 6:1. 
     
     
       22. The composition of claim 1 which is entirely free of hardener for said film-forming polymer. 
     
     
       23. A substrate coated in predetermined areas less than the entire area with the solder mask of claim 1. 
     
     
       24. The substrate of claim 23 wherein the coating thickness is about 1 to about 25 mils. 
     
     
       25. The method of claim 24 wherein the application of solder is conducted at a temperature of about 300° to about 400° C. 
     
     
       26. The substrate of claim 23 wherein the coating thickness is about 5 to about 10 mils. 
     
     
       27. The substrate of claim 23 wherein the coating thickness is about 2 to about 3 mils. 
     
     
       28. A method for protecting predetermined areas on a substrate from solder deposition which comprises: A. applying to predetermined areas less than the entire area of a substrate by screen printing a screenable and strippable mask composition containing: (1) a film-forming polymer portion in the form of a liquid composition wherein the film-forming polymer is a polyimide/amide or a liquid polyepoxide;   (2) a detackifier compatible with the polymer being selected from the group of (a) liquid silicone oil   (b) terpene   (c) terpineol   (d) drying oil, and   (e) mixtures thereof;     (3) a solid high temperature resistant filler in an amount sufficient to render the composition removable from the substrate after solder application      wherein the ratio of A:B is about 2:1 to about 1:3, and provided that when A is a polyepoxide liquid, B includes said silicone oil; and wherein said composition is at least substantially free of hardener from said film-forming polymer;   B. drying the coated substrate to thereby harden the composition;   C. applying solder whereby said solder does not adhere to those areas protected by the solder mask;   D. removing the solder mask.   
     
     
       29. The method of claim 28 wherein said solder mask is removed by contact with a solvent at elevated temperature. 
     
     
       30. The method of claim 28 wherein said elevated temperature is about 100° to about 180° C. 
     
     
       31. The method of claim 28 wherein said drying is conducted at a temperature of about 50° C. to about 150° C. 
     
     
       32. The method of claim 28 wherein said drying is conducted at a temperature of about 150° C. 
     
     
       33. The method of claim 28 wherein said composition is entirely free of hardener for said film-forming polymer.